1. Field of the Invention:
The present invention relates to a thin film transistor array, and more specifically to that used for a liquid crystal display panel.
2. Description of the Related Art:
The liquid crystal display panel has a thin film transistor array board in which a plurality of thin film transistors are disposed in a matrix form. Examples disclosing such thin film transistor arrays are U.S. Pat. No. 3,840,695 granted for Albert G. Fischer on Oct. 8, 1974 and Japanese Un-examined Patent Publication No. 61-5577. Each transistor in those thin film transistor arrays has the so-called inverse-staggered structure and is formed of a gate electrode disposed on a transparent insulator substrate, a first insulator film formed on the insulator substrate to cover the gate electrode, a semiconductor layer covering the first insulator film on the gate electrode, source and drain electrodes of metal contacting upper surface of the semiconductor layer, the source and drain electrodes being separate from each other to form a gap above the gate electrode, a second insulator film covering all the structure, and a light-shield layer formed on the second insulator film above the gap between the source and drain electrodes. Each of the source and drain electrodes is formed of two layers, that is, an ohmic contact layer and a wiring layer. First of the two wiring layers is connected to a pixel electrode formed in adjacent to the semiconductor layer. Second of the two wiring layers is formed commonly to connect the corresponding wiring layers of a line of thin film transistors in the matrix.
On the thin film transistor array board, a plurality of the semiconductor layers are disposed to form the matrix, the second wiring layer covering edges of the semiconductor layers. Therefore, if the second wiring layer is formed thin, the wiring layer easily generates an open-circuit at the edges of the semiconductor layers. In order to avoid the open-circuit the second wiring layer is usually made thick, for example, 2,000 .ANG.. If the second wiring layer is made thick, the second insulator film must be made thick, for example, 3,000 .ANG., to protect it from generation of many cracks at edges of the wiring layers. The cracks cause short-circuit between the light-shield layer and the source or drain electrodes. The thick film of the second insulator film simultaneously covers the pixel electrodes and lowers electric field applied to liquid crystal to deteriorate contrast of displayed image.